1. Field of the Invention
The present invention relates generally to tubular prostheses, such as grafts, stents, stent-grafts, and the like. More particularly, the present invention provides radially expansible tubular prosthesis structures which can be expanded up to predetermined limits to match individual body lumens, including blood vessels, particularly for the treatment of abdominal and other aneurysms.
Vascular aneurysms are the result of abnormal dilation of a blood vessel, usually resulting from disease and/or genetic predisposition, which can weaken the arterial wall and allow it to expand. While aneurysms can occur in any blood vessel, most occur in the aorta and peripheral arteries, with the majority of aortic aneurysms occurring in the abdominal aorta, usually beginning below the renal arteries and often extending into one or both of the iliac arteries.
Aortic aneurysms are most commonly treated in open surgical procedures where the diseased vessel segment is bypassed and repaired with an artificial vascular graft. While considered to be an effective surgical technique, particularly considering the alternative of a usually fatal ruptured abdominal aortic aneurysm, conventional vascular graft surgery suffers from a number of disadvantages. The surgical procedure is complex and requires experienced surgeons and well equipped surgical facilities. Even with the best surgeons and equipment, however, patients being treated frequently are elderly and weakened from cardiovascular and other diseases, reducing the number of eligible patients. Even for eligible patients prior to rupture, conventional aneurysm repair has a relatively high mortality rate, usually from 2% to 10%. Morbidity related to the conventional surgery includes myocardial infarction, renal failure, impotence, paralysis, and other conditions. Additionally, even with successful surgery, recovery takes several weeks, and often requires a lengthy hospital stay.
In order to overcome some or all of these drawbacks, endovascular prosthesis placement for the treatment of aneurysms has been proposed. Although very promising, many of the proposed methods and apparatus suffer from undesirable limitations. In particular, proper sizing of endovascular prostheses can be problematic.
Proper matching of the prosthesis to the blood vessel is critical to the treatment of an aneurysm. The prosthesis preferably extends axially beyond the weakened portion of the blood vessel to anchor securely in the healthy vessel wall. However, the cross-sectional size and axial length of individual blood vessels vary considerably between patients. Even within a patient, the cross-section and resilience of a lumen wall can vary considerably along its axial length, and the location and extent of the aneurysm will differ with different patients. Additionally, each prosthesis must be carefully constructed and handled, making it extremely costly to provide and maintain the large selection of prostheses required for proper fitting of every individual patient.
Known radially expandable intraluminal prostheses may generally be characterized as either resilient or plastically expanded structures. Resilient intraluminal prostheses are often formed as stent-grafts having self-expanding frames or xe2x80x9cstentsxe2x80x9d which radially conform to variations in lumenal cross-sections. Such resilient stent-grafts must expand against the luminal wall with sufficient force to anchor the prosthesis within the body lumen, and should ideally be sealed around the perimeter of the luminal wall to prevent leakage. Resilient prostheses which are too small may not expand sufficiently to seal or anchor properly, while oversized resilient prostheses can exert excessive pressure against the surrounding body lumen. Plastically expandable intraluminal prostheses have malleable frames which are expanded to fit the lumen when implanted, but the expanded prosthesis generally takes the cylindrical shape of the expanding balloon catheter, rather than conforming to irregular luminal cross-sections. Additionally, the expanded prostheses must be sufficiently large and rigid to provide a stable anchor and perimeter seal, requiring distension of the lumen adjacent the disease condition. Hence, even with proper fitting, most resilient or plastically expandable prostheses impose some stress on the body lumen. A still further complication arises from the use of a separate liner or xe2x80x9cgraft,xe2x80x9d which is often woven from inexpansible polyesters such as Dacron, and which may therefore wrinkle and occlude the lumen if the stent graft is not fully expanded.
It has previously been proposed to use radially expansible liners with plastically expansible stents so that the liner and the frame may be expanded together within a body lumen. In particular, liner materials having undrawn or partially drawn yarns in the circumferential direction allow concurrent plastic expansion of the liner and frame using a balloon catheter. Such liner materials would thus facilitate in situ expansion of plastically expandable stent-grafts within a wide range of sizes. Unfortunately, because of the great expansibility of partially drawn yarns, any bulges formed by uneven expansion of the liner material may continue to expand in an uncontrolled manner during deployment or size adjustment. Such bulges in the liner may even result in a weak, oversized region that could potentially collect thrombus or even fail during deploymentxe2x80x94effectively resulting in an aneurysm of the prosthesis. Furthermore, such bulges in an endoluminal prosthesis may cause folds of the liner material, leading to leakage between the prosthesis and the vessel wall.
Known prostheses having plastically expansible liner materials may suffer from additional disadvantages. As described above, such prostheses generally also include frames which are rigid when expanded, typically relying on distension of the body lumen around a cylindrical frame to anchor and seal the prosthesis. Furthermore, undrawn or partially drawn liners may be inadvertently overexpanded, resulting in xe2x80x9ccreepingxe2x80x9d of the material, changes in porosity, or even the creation of open fistulas. Any such overexpansion of the liner might well go undetected, as in situ expansion is generally a fluoroscopically directed process in which the condition of the liner is not easily monitored.
In co-pending U.S. patent application Ser. No. 08/538,706, which is assigned to the assignee of the present application, the full disclosure of which is incorporated herein by reference, describes a resiliently expandable prosthesis which includes a plastically expansible liner with a resilient frame, in which the resilient expansion of the frame is restrained by the liner. Advantageously, such a liner-restrained structure allows in situ expansion of the liner to match the perimeter of the surrounding body lumen, and also allows the fitted prosthesis to resiliently conform to irregular lumenal cross-sections. Application Ser. No. 08/538,706 also teaches the selective expansion of xe2x80x9csealing cuffs,xe2x80x9d integral or separate prosthetic end seals, which preferably include expansible liner materials to facilitate sealing and conforming an end of a tubular prosthesis against the surrounding body lumen wall. The use of liner materials with partially oriented yarns was suggested for these liner-restrained prostheses and sealing cuffs.
Although the liner-restrained prostheses, sealing cuffs, and partially drawn yarns described above provide substantial advantages over other endoluminal prosthetic structures, still further refinements are desirable. In general, it would be desirable to provide improved prostheses, including grafts and stent-grafts, and improved methods for placement of such prostheses to treat aneurysms and other conditions. It would be particularly desirable to provide liner materials for use in liner-restrained and other endoluminal prosthetic structures which would allow the prosthesis to expand plastically within a preset range, but which would reduce the danger of overexpansion. It would further be advantageous to provide liner materials which would allow controlled, selective expansion of portions of the prosthesis to promote anchoring or sealing, but which would resist expansion in alternative portions, particularly adjacent a weakened portion of a body lumen.
2. Description of the Background Art
U.S. Pat. No. 5,443,499 describes a radially expandable tubular prosthesis formed with radial yarns which are at most partially drawn. The prosthesis may optionally be secured to a body lumen through simultaneous balloon expansion of the prosthesis and an attached stent. French Patent Application Publication No. FR 2,714,816 describes a vascular prosthesis including a sleeve which contracts axially when stretched radially. Sliding connections are provided between a support structure and the sleeve, and additional material is preferably provided to compensate for axial contraction of the sleeve. Similarly, U.S. Pat. No. 5,064,435 describes a self expanding prosthesis which maintains a stable axial length during expansion by anchoring of radially outward flares at each end, and by sliding of an overlapping medial region therebetween. U.S. Pat. No. 4,834,755 describes a triaxially-braided fabric prosthesis structure to provide controlled strength and elasticity. U.S. Pat. No. 5,456,713 is generally relevant.
U.S. Pat. No. 5,258,042 describes an intravascular hydrogel implant which expands when hydrated. U.S. Pat. No. 5,470,313 describes a variable diameter balloon dilation catheter having a pressure controlled inflation profile.
The present invention provides radially expansible tubular prostheses, particularly grafts, stents, and stent-grafts, for the treatment of aneurysms, stenoses, and other disease conditions. The expansible prostheses of the present invention may be tailored by selective mechanical expansion of limited regions of the prosthesis, or may alternatively be uniformly radially expanded, depending upon the specific requirements of the patient. Advantageously, in situ expansion is generally limited by an element of the prosthesis, e.g., by inelastic circumferential fibers of a prosthetic liner, or by a circumferential element of the frame which limits expansion, so as to avoid overexpansion of a portion of the liner. Such a self-limiting expansible structure will thus minimize the possibility of over-expanding the prosthetic lumen.
The controlled expansion of the present prostheses is generally limited by a structural element of the prosthesis itself. Hence, a stent-graft according to the invention will freely expand, either resiliently or plastically, only to some predetermined expansion limit, at which limit an element of either the liner or the frame (or both) impedes further expansion. In some cases, the expansion limit will be present in or provided on the interface between the liner and the frame, for example, a circumferential band of suture or other material which both limits stent-graft expansion and connects the liner to the frame.
The expansion limit itself may provide either a fixed radial limit or an intermediate limit. A fixed limit prevents any significant expansion of the prosthesis beyond a maximum safe distention cross-section for the body lumen, regardless of the expansive radial force applied to the prosthesis. Such a fixed limit may also help to prevent local or global porosity of the liner from exceeding a desired maximum, to avoid the creation of fistulas, and to promote even expansion of the prosthesis, rather than bulging of any weak regions. Intermediate expansion limits will provide some mechanism which allows expansion to continue beyond an initial limit, for example, by incorporating a frangible or plastic reinforcing element in the frame or liner which fails or plastically deforms under a threshold expansive force. Intermediate limits thereby provide the safety of an expansion limitation, but with the added option of continued expansion when justified. Optionally, a plurality of intermediate limitations may be used in series, or in combination with a fixed limit.
In a first aspect, the present invention provides a controlled expansion endoluminal stent-graft comprising a radially expansible tubular frame and a plastically expansible liner on the frame. Either the frame or the liner includes a reinforcing element which limits expansion of the stent-graft at a predetermined expanded size. Generally, the reinforcing element is included in the liner as circumferentially oriented yarn. A particularly advantageous reinforced liner includes composite circumferential yarns having inexpansible fibers wrapped around an expansible fiber, such as a partially oriented fiber, PTFE, or the like. In other embodiments, the reinforcing element restrains the frame, for example, by limiting the expansion of individual perforations on a perforate frame structure.
As used herein, xe2x80x9cexpansiblexe2x80x9d generally refers to both self-expanding structures which increase in dimensions when released from compression or subjected to a change of state (e.g., shape recovery of shape memory alloys), and also to structures which deform plastically when subjected to expansive stress. Hence, both resilient and plastically expansible (sometimes called malleable) stents are encompassed by the term xe2x80x9cexpansible frames.xe2x80x9d In contrast, xe2x80x9cplastically expansiblexe2x80x9d herein more specifically refers to structures which plastically increases in dimension when under an expansive force.
In another aspect, the present invention provides an expansible liner stent-graft comprising a radially expansible tubular frame and a plastically expansible liner on the frame. In contrast to known expansible liner materials, the liner here comprises a fill element including fully drawn fiber which defines a maximum expanded perimeter of the liner. The fully drawn fiber may optionally wind around another fiber so as to straighten during expansion, or may alternatively be texturized or annealed after it is drawn. Advantageously, such fibers will substantially retain the ultimate strength of the fully drawn fiber.
As used herein, a xe2x80x9cfill elementxe2x80x9d means fiber, monofilament, fiber within a thread, fiber within a yarn, a thread within a yarn, or, alternatively, a yarn itself, which forms a circumferentially oriented element of the liner material.
In another aspect, the present invention provides a limited expansion graft comprising a fabric which includes composite yarns. The composite yarns include both serpentine inexpansible fiber and expansible fiber so that the inexpansible fiber straightens when the graft is intentionally expanded. The straightening inexpansible fiber gradually becomes taut, thereby preventing expansion of the graft beyond a predetermined limit. Preferably, the inexpansible fiber is wound over the expansible fiber. Advantageously, the expansible fiber or xe2x80x9ccorexe2x80x9d generally maintains structural integrity of the liner to prevent inadvertent deformation or distention of the prosthesis under the stresses of ordinary use.
The present invention also provides a method for deploying an endoluminal prosthesis at a target site within a diseased body lumen, the method comprising positioning the prosthesis at the target site, at which a liner of the prosthesis is plastically expanded. Advantageously, the plastic expansion of the liner is limited to a predetermined size by an element of the prosthesis.
In another aspect, the present invention provides a method for deploying an endoluminal prosthesis at a target site within a diseased body lumen, the method comprising introducing the prosthesis into the body lumen and positioning the prosthesis at the target site. A phase of a reinforcement element of the prosthesis is altered at the target site to increase expansibility of the element, and the cross-section of the prosthesis is expanded while the phase remains altered. The phase of the reinforcement element is then returned to reduce expansibility. Generally, the phase altering step comprises changing a temperature of a temperature sensitive polymer, which is ideally included in a circumferentially oriented fiber and woven into a prosthesis liner.
In another aspect, the present invention provides a method for producing a radially expansible graft, the method comprising drawing fiber to a fully drawn length and then texturizing the drawn fiber. The texturized fiber may then be woven into a tube so that the fiber is circumferentially oriented.
In yet another aspect, the present invention provides a method for producing a radially expansible graft, the method comprising drawing fiber to a fully drawn length and annealing the drawn fiber. The fiber is preferably woven into a tube so that the fiber is circumferentially oriented.
In yet another aspect, the present invention provides a cuffed endoluminal stent-graft comprising a radially expansible tubular frame and a liner disposed on an inner or outer surface of the frame. Expansion of the stent-graft along the liner is limited to a predetermined expanded cross-section. A sealing cuff is disposed adjacent to the liner end to extend radially beyond the liner and seal between the liner and a surrounding body lumen.
In a final aspect, the present invention provides a sealing device for use with an endoluminal prosthesis, said sealing device comprising a fabric having partially oriented yarn so that the fabric is plastically expansible to seal between the prosthesis and a surrounding body lumen.